Chemical warfare

Chemical warfare is warfare (and associated military operations) using the toxic properties of chemical substances to kill, injure or incapacitate the enemy.

Chemical warfare technology

Although crude chemical warfare has been employed in many parts of the world for thousands of years, "modern" chemical warfare began during World War I. Initially, only well-known commercially available chemicals and their variants were used. These included chlorine and phosgene gas. The methods of dispersing these agents during battle were relatively unrefined and inefficient.

Related Topics:
World War I - Chlorine - Phosgene

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Germany, the first side to employ chemical warfare on the battlefield, simply opened canisters of chlorine upwind of the opposing side and let the prevailing winds do the dissemination. Soon after, the French modified artillery munitions to contain phosgene – a much more effective method that became the principal means of delivery.

Related Topics:
Germany - French - Artillery - Munition

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Since the development of modern chemical warfare in World War I, nations have pursued research and development on chemical weapons that falls into four major categories: new and more deadly agents; more efficient methods of delivering agents to the target (dissemination); more reliable means of defense against chemical weapons; and more sensitive and accurate means of detecting chemical agents.

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Chemical warfare agents

A chemical used in warfare is called a chemical warfare agent (CWA), and is usually gaseous at room temperature or is a liquid that evaporates quickly. Such liquids are said to be volatile or have a high vapor pressure. The resulting fumes are toxic, hence the phrase "poison gas" used to describe a chemical weapon deployed in gaseous form. Many chemical agents are made volatile so they can be dispersed over a large region quickly.

Related Topics:
Gas - Vapor pressure

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The earliest target of chemical weapon agent research was not toxicity, but development of agents that can affect a target through the skin and clothing, rendering protective gas masks useless. In July 1917, the Germans first employed mustard gas, the first agent that circumvented gas masks. Mustard easily penetrates leather and fabric to inflict painful burns on the skin.

Related Topics:
Gas mask - 1917 - Mustard gas

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Persistency

All chemical weapon agents are classified according to their persistency, a measure of the length of time that a chemical agent remains effective after dissemination. Chemical agents are classified as persistent or nonpersistent.

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Agents classified as nonpersistent lose effectiveness after only a few minutes or hours. Purely gaseous agents such as chlorine are nonpersistent, as are highly volatile agents such as sarin and most other nerve agents. Tactically, nonpersistent agents are very useful against targets that are to be taken over and controlled very quickly. Generally speaking, nonpersistent agents present only an inhalation hazard.

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By contrast, persistent agents tend to remain in the environment for as long as a week, complicating decontamination. Defense against persistent agents requires shielding for extended periods of time. Non-volatile liquid agents, such as blister agents and the oily VX nerve agent, do not easily evaporate into a gas, and therefore present primarily a contact hazard.

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Classes of chemical warfare agents

Chemical warfare agents are organized into several categories according to the manner in which they affect the human body. The names and number of categories varies slightly from source to source, but in general, types of chemical warfare agents are as follows:

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There are other chemicals used militarily that are not technically considered to be "chemical weapon agents," such as:

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• Defoliants that destroy vegetation, but are not immediately toxic to human beings. (Agent Orange, for instance, used by the United States in Vietnam, contained dioxins and is known for its long-term cancer effects and for causing genetic damage leading to serious birth deformities.)
• Incendiary or explosive chemicals (such as napalm, extensively used by the United States in Vietnam, or dynamite) because their destructive effects are primarily due to fire or explosive force, and not direct chemical action.
• Viruses, bacteria, or other organisms, or their toxic products. Their use is classified as biological warfare.

Chemical weapon designations

Most chemical weapons are assigned a one- to three-letter "NATO weapon designation" in addition to, or in place of, a common name. Binary munitions, in which precursors for chemical weapon agents are automatically mixed in shell to produce the agent just prior to its use, are indicated by a "-2" following the agent's designation (for example, GB-2 and VX-2).

Related Topics:
NATO - Binary munition

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Some examples are given below:

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Chemical agent delivery

The most important factor in the effectiveness of chemical weapons is the efficiency of its delivery, or dissemination, to a target. The most common techniques include munitions (such as bombs, projectiles, warheads) that allow dissemination at a distance and spray tanks which disseminate from low-flying aircraft. Developments in the techniques of filling and storage of munitions have also been important.

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Although there have been many advances in chemical weapon delivery since World War I, it is still difficult to achieve effective dispersion. The dissemination is highly dependent on atmospheric conditions because many chemical agents act in gaseous form. Thus, weather observations and forecasting are essential to optimize weapon delivery and reduce the risk of injuring friendly forces.

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Dispersion

Dispersion is the simplest technique of delivering an agent to its target. It consists of placing the chemical agent upon or adjacent to a target immediately before dissemination, so that the material is most efficiently used.

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World War I saw the earliest implementation of this technique, when German forces simply opened canisters of chlorine and allowed the wind to carry the gas across enemy lines. While simple and easy, this technique had numerous disadvantages. Delivery depended greatly on wind speed and direction. If the wind was fickle, as at Loos, the gas could blow back, causing friendly casualties. Gas clouds gave plenty of warning, allowing the enemy time to protect themselves, though many soldiers found the sight of a creeping gas cloud unnerving. Also gas clouds had limited penetration, capable only of affecting the front-line trenches before dissipating. Although it produced limited results in World War I, this technique shows how simple chemical weapon dissemination can be.

Related Topics:
World War I - Loos

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Shortly after this "open canister" dissemination, French forces developed a technique for delivery of phosgene in a non-explosive artillery shell. This technique overcame many of the risks of dealing with gas in cylinders. First, gas shells were independent of the wind and increased the effective range of gas, making any target within reach of guns vulnerable. Second, gas shells could be delivered without warning, especially the clear, nearly odorless phosgene — there are numerous accounts of gas shells, landing with a "plop" rather than exploding, being initially dismissed as dud high explosive or shrapnel shells, giving the gas time to work before the soldiers were alerted and took precautions.

Related Topics:
Phosgene - Artillery - High explosive - Shrapnel

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The major drawback of artillery delivery was the difficulty of achieving a killing concentration. Each shell had a small gas payload and an area would have to be subjected to saturation bombardment to produce a cloud to match cylinder delivery.

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Over the years, there were some refinements in this technique. In the 1950s and early 1960s, chemical artillery rockets contained a multitude of submunitions, so that a large number of small clouds of the chemical agent would form directly on the target.

Related Topics:
1950s - 1960s

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Thermal dissemination

Thermal dissemination is the use of explosives or pyrotechnics to deliver chemical agents. This technique, developed in the 1920s, was a major improvement over earlier dispersal techniques, in that it allowed significant quantities of an agent to be disseminated over a considerable distance. Thermal dissemination remains the principal method of disseminating chemical agents today.

Related Topics:
Explosive - Pyrotechnic - 1920s

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Most thermal dissemination devices consist of a bomb or projectile shell that contains a chemical agent and a central "burster" charge; when the burster detonates, the agent is expelled laterally.

Related Topics:
Bomb - Projectile shell

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Thermal dissemination devices, though common, are not particularly efficient. First, a percentage of the agent is lost by incineration in the initial blast and by being forced onto the ground. Second, the sizes of the particles vary greatly because explosive dissemination produces a mixture of liquid droplets of variable and difficult to control sizes.

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The efficacy of thermal detonation is greatly limited by the flammability of some agents. For flammable aerosols, the cloud is sometimes totally or partially ignited by the disseminating explosion in a phenomenon called flashing. Explosively disseminated VX will ignite roughly one third of the time. Despite a great deal of study, flashing is still not fully understood, and a solution to the problem would be a major technological advance.

Related Topics:
Aerosol - VX

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Despite the limitations of central bursters, most nations use this method in the early stages of chemical weapon development, in part because standard munitions can be adapted to carry the agents.

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Aerodynamic dissemination

Aerodynamic dissemination is the non-explosive delivery of a chemical agent from an aircraft, allowing aerodynamic stress to disseminate the agent. This technique is the most recent major development in chemical agent dissemination, originating in the mid-1960s.

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This technique eliminates many of the limitations of thermal dissemination by eliminating the flashing effect and theoretically allowing precise control of particle size. In actuality, the altitude of dissemination, wind direction and velocity, and the direction and velocity of the aircraft greatly influence particle size. There are other drawbacks as well; ideal deployment requires precise knowledge of aerodynamics and fluid dynamics, and because the agent must usually be dispersed within the boundary layer (less than 200–300 ft above the ground), it puts pilots at risk.

Related Topics:
Aerodynamics - Fluid dynamics - Boundary layer

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Significant research is still being applied toward this technique. For example, by modifying the properties of the liquid, its breakup when subjected to aerodynamic stress can be controlled and an idealized particle distribution achieved, even at supersonic speed. Additionally, advances in fluid dynamics, computer modeling, and weather forecasting allow an ideal direction, speed, and altitude to be calculated, such that weapon agent of a predetermined particle size can predictably and reliably hit a target.

Related Topics:
Computer model - Weather forecasting

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